Advanced Corona Ignition - ACIS - Plasma instead of spark

Spark plugs have been in cars since the very beginning, and their first application began as early as 1860, long before the first car. Although they have been perfected over time, the basic principle has remained the same: an electric spark that jumps between two electrodes causes ignition of a mixture of gasoline and air, whose further combustion creates high pressure and temperature and pushes the piston or mechanical work.

In an effort to increase engine efficiency, ie reduce the consumption and amount of harmful gases in the exhaust, while increasing power, the spark plug is increasingly becoming a limiting factor despite numerous improvements over decades of engine development. One of the alternative solutions that offers promising progress with almost no changes in engine design is the so-called. Advanced Corona Ignition System or ACIS.

It is an advanced system of ignition of the mixture with the help of plasma and it was developed by the American factory Federal Mogul, which is one of the largest manufacturers of components for cars. In addition to offering a completely different way of igniting the mixture, ACIS enables (at least according to Federal Mogul) lower fuel consumption by up to 10 percent. How?

The classic spark plug works by igniting a compressed mixture of gasoline and air at one, usually the center point (although there are also engines with two spark plugs). From this point, the combustion front expands towards the edges of the cylinder causing an increase in pressure and temperature and a displacement of the piston in the operating stroke. ACIS replaces the spark plug in a way that creates a larger source of ignition of the crown-shaped mixture (hence the word Corona in the name, which has nothing to do with Mexican beer) around its top.

This results in ionization of the mixture inside the cylinder and initiation of much faster and more efficient combustion in a much larger area around the tip of the spark plug. Extremely hot plasma that is produced is able to ignite high quality and more flammable mixtures, such as those produced by the engine with poor mixture or use exhaust gas recirculation (EGR).

The spark created by a classic spark plug lasts two to three milliseconds, while the plasma discharge is much shorter, only 100 to 200 microseconds, but it is also much more intense and instead of happening at one point, the crown can be up to 30 or 40 mm in diameter. This means that combustion takes place almost simultaneously in the entire cylinder, which opens the possibility for engineers to design the combustion chamber differently in the future. And with the existing construction of the engine, the advantages are obvious: the mixture burns faster and more efficiently, and it is very important that it is possible to burn quality of the poor mixture, which regularly monitors the operation of the engine at lower load.

This means that running the engine at constant speed on the highway could be spectacularly economical. Equally, the use of ACIS allows for an even larger diameter of combustion gas per cylinder (EGR) which significantly reduces the amount of nitrogen oxide (NOx) and unburnt hydrocarbons in the exhaust. This is otherwise widely used in diesel engines because the method of ignition of the mixture is different, and plasma now allows it in gasoline engines.

Also, the need for a very rich mixture decreases with a sudden increase in engine load. ACIS also reduces the possibility of detonation or uncontrolled combustion in the cylinder. Detonation, ie self-ignition of the mixture occurs when the shock wave of pressure begins to spread towards the edges of the cylinder where high pressure and temperature cause self-ignition of the mixture like that in a diesel engine, which leads to improper engine operation.

Because the plasma is expanding at a high speed and on a larger surface almost instantaneous ignition of all fuel molecules occurs, which prevents the occurrence of detonation. This is especially important because it enables the application of a higher degree of compression to gasoline engines, which is significantly more efficient, but also causes detonation problems (which ACIS successfully solves). The compression ratio can be easily increased to 14: 1 for atmospheric engines and 12: 1 for turbo engines.

It is not unimportant that the new "spark plugs" still last, because there are no parts that are worn out here as with classic spark plugs whose electrodes are damaged by electro erosion, so it is necessary to change them. ACIS is still in the development phase, but there are already prototypes that can replace spark plugs in existing engines, but real progress will be made with the development of engines for the use of ACIS.

A conventional spark plug needs a very high voltage to generate a spark, and its values ​​are up to 30.000 V, and often more. ACIS does not need such a high voltage, but works on the principle of extremely fast resonance, which excites air and fuel ions. In order to generate the current required for ionization, a 12 V car power supply is first raised to 150 V, and then a frequency transformer is generated on a 1 kV square wave that is fed to a coil and a capacitor. This creates a resonant circuit that emits an electromagnetic wave with a frequency of 1 MHz, a short signal that allows very precise control of the ignition time of the mixture.